In resistance or flash welding of sheet or strip, electrical current is caused to flow through the strip by means of two opposed electrodes. Contaminants, found on the surface of the strip, can become trapped between the strip and the electrodes during the welding cycle and adhere to the electrode face creating hot spots which cause localized melting of the electrodes. When this happens, molten copper from the electrodes is deposited upon the surface of the strip and these contaminated areas become very hard or brittle causing cracks and/or holes during the cold reduction of the ferrous strip. Occasionally tears initiate from these defects and propagate through the sheet or strip.
Pits, formed in the electrode's face where copper has been melted away, can continue to form hot spots and are enlarged with subsequent welding cycles. This repeated localized melting of the electrodes causes reduced electrode service life and premature mill shutdown for electrode reconditioning.
Flash welders installed along continuous pickling lines are subjected to an extraordinary amount of dirt and contaminants. Mill scale, oils and water are dragged onto the electrode faces by the strip. In addition, grit created from the molten metal expelled during the welding cycle falls onto the electrode faces in the form of contaminants. The wear on welding electrodes in such an environment is extreme due to hot spots caused by the contaminating materials and the short electrode service life causes frequent mill shutdowns.